Cut-off switch



Aug. 8, 1961 A. A. H. SOUCHET CUT-OFF SWITCH Filed June 18. 1958 Unitednitrates Patent 2,995,638 CUT-OFF SWITCH Andr A. H. Souchet, Nanterre,France, assignor to La Telemecanique Electrique (Societe Anonyme),Nanterre, France, a French company Filed June 18, 19 58, Ser. No.742,869 Claims priority, application France July 3, 1957 5 Claims. (Cl.200-147) This invention relates to cut-off switch arrangements and itsgeneral object is to provide a cut-off switch including improved meansfor quenching the are occurring on separation of the switch contacts.

The invention is especially, though not exclusively, applicable tocut-off switch arrangements wherein fiat switch contacts are carried inmutually opposed relationship at adjacent ends of two flat strip likeconductors extending in generally reverse directions to each other awayfrom said adjacent contact-bearing ends, and wherein the contact makingand breaking displacements involve a displacement of one of saidconductors towards and away from the other, normally to the plane of thecontact elements.

A known are quenching expedient sometimes used in connection with suchcut-off switches involves the provision of metal plate elements disposedsymmetrically on opposite sides of said contacts in spaced relationtherewith and extending in planes generally normal to the planes of saidcontacts. The arc-quenching action of such a device relies on the factthat the magnetic field present around the arc cooperates with themagnetic characteristics of the plate to generate a magnetomotive forcewhich tends to shift the arc towards one or the other plate, whereuponthe arc is rapidly quenched, mainly due to the cooling eflfect of theplate.

In practice however such are quenching devices have not been fullysatisfactory since it is found that the are frequently tends to dwell arelatively long period of time across the contacts of the switch beforeit finally shifts one way or the other towards one of the plates to bequenched thereby. It has now been found by applicant that thisundesirable condition in which the quenching of the arc is delayed,occurs whenever the random points of the contact surfaces at which thearc first initiates, happen to be positioned substantially at equaldistances from both side quenching plates, so that the arc is at suchtimes subjected to substantially equal and opposite forces in bothdirections and as a consequence remains substantially stationary untilone or the other force predominates.

The invention is based on the finding just stated and in accordancetherewith achieves improved arc quenching action in a cut-off switch byproviding a quenching member on only one side of the switch contacts. Itwill be understood that in such conditions no matter where the arehappens to originate over the entire surfaces of the contact elements,it will be urged by the electromagnetic forces only in the direction ofsaid one side, and will under no circumstances tend to dwell in thecentral area of the contact surfaces. Greatly improved arc quenchingaction is thus obtained.

The invention therefore provides a cut-off switch arrangement having apair of opposed generally flat contact elements movable into and out ofengagement with each other in a direction generally normal to the planeof said elements, and a metallic member adjacent to only one side ofsaid contact elements and spaced therefrom, whereby a cut-off areoccurring on disengagement of said elements will tend to shift laterallytowards said member to be quenched thereby.

In a preferred construction the member is in the form ice of anangularly bent plate having two portions at right angles to each otherrespectively extending alongside a longitudinal and transverse side edgeof both contact elements. According to a further advantageous feature,the contact elements are supported on respective fiat striplikeconductors at positions laterally displaced from the longitudinalmidline of said conductors towards said metallic quenching member. It isfound that the further dissymmetry thus introduced is accompanied by acorrespondingly increased dissymmetry in the magnetomotive forces actingon the arc and that the quenching action is thus further accelerated.Furthermore, the longitudinal side of each contact element remote fromthe metallic quenching member is preferably provided beveled.

The invention further includes within its scope the application of theabove specified cut-off switch arrangement to circuit breaker switchdevices of the type including a movable bridging conductor memberdisplaceable into and out of contacting cooperation with a pair ofspaced contacts. Such devices are advantageous in that the cut-off arcis divided into two smaller arcs of weaker energy content.

Exemplary embodiments of the invention will now be described forpurposes of illustration but not of limitation with reference to theaccompanying drawings, where- 1n:

FIG. 1 is a perspective view of a conventional cut-off switcharrangement;

FIG. 2 is a plan view of one contact of the conventional arrangementshown in FIG. 1;

FIG. 3 is a plan view of an arrangement according to the invention in asimple construction form;

FIG. 4 is a perspective view of a cut-off switch arrangement accordingto the invention in a more elaborate form thereof;

FIG. 5 is a section on line VV of FIG. 4.

FIG. 5a is a similar view relating to a modification;

FIG. 6 is a perspective view illustrating the application of theinvention to a bridge type circuit breaker; and

FIG. 6a is a similar view of a modified construction.

As shown in FIG. 1, a conventional cut-off switch arrangement of thegeneral type to which this invention relates comprises a pair ofparallel flat conductor bars or strips 1 and 2 extending in generallyopposite directions and having secured to the adjacent ends of them infacing relationship, the respective rectangular contact lugs 1a and 2a.The contact lugs are adapted to be pressed against each other forestablishing the circuit and separated for breaking the circuit, bydisplacement of conductor 2 as indicated by the arrow 0.

In such an arrangement the current, at an instant of time, can berepresented by the chain-line arrows indicated as passing from conductor1 to conductor 2. This current path includes three sections: section 3extending through conductor '1, section 3a which is constituted by anarc discharging across the contacts, and a third section 3 alongconductor 2.

In this circuit path, the arc section 3a is freely movable under theinfluence of the fields generated by the sections 3 and 3 The fieldforces generated by these sections and acting on the are 3a arerespectively indicated as F and F The are itself generates a symmetricfield surrounding it, and because of this symmetry this field'has noinfluence upon the path followed by the are.

In the conventional construction shown in FIG. 1 therefore, there shouldapparently not be any tendency for the arc to be shifted transversely.However, as shown in FIG. 2, should the are be struck at a positiondisplaced from the plane XX which is the plane of symmetry of thecontacts, for instance at the position A, the linear current pathsindicated as the broken lines 4 in each of the conductors 1 and 2, arebent in dissymmetrical fashion in 3 both conductors and it will be seenthat this will result in a transverse force F being generated tending toincrease further the displacement of the are away from the X-X plane.The same effect obviously is present to either side of the plane ofsymmetry.

The invention proposes, in efifect, to increase and develop thisdissymmetry effect in order to force the arc to reach surrounding metalsurfaces of the assembly to be thereby cooled, damped and quenched.

For this purpose as shown in FIG. 3, there is arranged adjacent thecontact lugs 1a and 2a an element of magnetic sheet material 5 bent atright angles so as to comprise two flanges both parallel to thedirection of relative displacements of the contacts towards and awayfrom each other, so as to enclose said contacts on two sides thereof,while the remaining two sides are free. With this arrangement, themagnetic field H which surrounds the arc present at the position A isrendered dissymmetrical due to the presence of the flanges of themagnetic element 5, so that only the field components such as H and Hare effective. The field components generate the magnetomotive forces F,and P which act to displace the arc towards the element 5. The are thenbecomes caught on the surface of the element and is quenched due tostrong cooling effect.

As previously indicated, such an action would be facilitated if the arcwere to assume dissymmetrical initial position towards the magneticelement 5. In order to increase this effect of dissymmetry, as shown inFIG. 4, the contacts 1a and 2a may be arranged dissymrmetrically at theends of the respective conductors 1 and 2, i.e. displaced towards theelement 5. With this arrangement, the distribution of the lines ofcurrent flow across the contacts is such as to provide an initialdissyrnmetry in the forces at the instant the are is generated, and thusaccelerates the displacement of the arc ends towards the quenchingelement.

The dissymmetrical efi'ect described can further be emphasized byforming both rectangular contact lugs with bevel side portions 6 over atleast that side edge of each contact remote from the element 5. Inpractice, it is suflicient if such a bevel is formed on the edge of thecontact remote from element 5 and parallel to the direction of theconductors 1 and 2.

In such conditions, as shown in FIG. 5, the arc originating across thecontacts 1a and 2a as the contacts separate, rapidly progresses towardsthe edges of the contacts directed towards the element 5, and breaksdown into two smaller arcs A and A between the edge of each contact andthe element.

The sharp drop in anode and cathode voltages at the points 7 and 8 atwhich the are is engaging the sheet element causes a corresponding dropin the energy of the component arcs. This, together with the increase inlength of the arc as it is displaced out of its normal path across thecontact, and the cooling action of the element, rapidly damps out thearc and thus increases the cut-off capacity of the switch.

In case of a cut-off switch enclosed within a casing of e.g. plasticmaterial, the angular metallic element will simultaneously serve toprotect the wall of the casing and prevent damage of its by the arc.

FIG. 6 illustrates the application of the invention to a bridge contactarrangement in a circuit breaker or similar cut-off switch apparatus. Asshown the bridging member 9 is operated through the insulated rod 10 soas to be displaced in the direction indicated by the arrow 0 to breakthe circuit, and displaced in the opposite direction to establishconnection between the conductors 11 and 12. The bridging member carriesthe contact lugs 9a and 9b at its respective ends, and the conductors'11 and 12 carry the cooperating contact lugs 11a and 12a. Eachcooperating pair of contact lugs 9a-11a, and 9b- 12a, is surrounded ontwo sides by a related angular metallic element 13 or 14. Moreover eachsaid cooperating s contact pair is displaced laterally to one side ofthe related conductors towards the related metal element. That edge ofeach contact lug directed away from the parallel flange of the relatedelement and parallel to the direction of the conductors is bevelled.Adjacent each bevel edge of each contact lug a free area such as 15 isdefined on the related conductor, while the opposite edge of the contactlug extends flush with the adjacent edge of the conductor, or may evenproject beyond the conductor edge as indicated in FIG. 5a.

In the arrangement of FIG. 6 just described, it will be noted that theangular metal elements 13 and 14 are arranged in mutually opposedrelation, so that they may be rigidly secured to or form part ofopposite casing walls of a common casing enclosing the switch device.Further, the opposed relationship between the elements 13 and 14 resultsin the bridging member 9 being symmetrical, so that it can be rotatedabout its vertical axis without impairing the operation of the switch.While this may have its advantages in facilitating the assembly of thedevice, it will be evident that such construction is not essential andthat instead the arrangement shown in FIG. 6a may be used, wherein bothangular elements 13 and 14 are disposed on the same side of the bridgemember, and where consequently the free areas 15 of the conductors wouldalso lie on the same side.

Various other modifications will be apparent to those familiar with theart within the scope of the invention.

What I claim is:

1. A cut-off switch comprising a pair of conductor strips extendingendwisely in opposite directions, a pair of generally flat contact lugson adjacent ends of said strips, with flat contact faces of said lugs inface-to-face relationship, said strips being relatively movable in adirection normal to said contact faces to move said faces into and outof interengagement, and arc-quenching means of metallic magneticmaterial spaced from said strips and lugs and disposed at only one ofopposite sides of said conductor strips; the spacing of said means fromany are formable between said lugs being such as to cause attraction ofthe arc to said means, free of counter-attraction from the other of theopposite sides of the conductor strips, said conductor strips being offlat material and disposed with adjacent ends thereof in overlappingrelation, said arc-quenching means comprising a member of magnetic sheetmetal of L-shape in section, the legs of the L extending in planesnormal to the planes of said contact faces, one of said legs being atsaid only one of opposite sides of said conductor strips, and the otherof the legs of the L extending transversely of said strips in opposedrelation to the end of one of said strips and to said contact lugs.

2. A cut-off switch comprising a pair of conductor strips extendingendwisely in opposite directions, a pair of generally flat contact lugson adjacent ends of said strips, with flat contact faces of said lugs inface-to-face relationship, said strips being relatively movable in adirection normal to said contact faces to move said faces into and outof interengagement, and arc-quenching means of metallic magneticmaterial spaced from said strips and lugs and disposed at only one ofopposite sides of said conductor strips; the spacing of said means fromany are formable between said lugs being such as to cause attraction ofthe are to said means, free of counter-attraction from the other of theopposite sides of the conductor strips, said contact lugs beinggenerally rectangular and said arc-quenching means having two flatsurfaces in rightangular interrelation, one of said flat surfaces beingat said only one of opposite sides of said conductor strips and theother of said fiat surfaces extending transversely of said stripsadjacent to said contact lugs and to the end of one of said strips.

3. A cut off switch comprising a pair of coplanar conductor stripsextending endwisely in opposite directions, flat, rectangular, firstcontact elements carried by the nearest end portions of said strips, aconductive bridging member movable normally to the plane of said strips,second contact elements carried toward opposite ends of said bridgingmember and arranged to conductively engage said first contact elementsupon such movement of the bridging member, and two separate L-shapedarc-quenching members of magnetic metal disposed separately inarc-attracting association with each pair of such conductivelyengageable contact elements, each of said arcquenching members havingflanges, normal to the plane of said strips and a first of said flangesbeing adjacent to corresponding sides of said strips and bridging memberand a second of said flanges being adjacent to an opposed end of saidbridging member.

4. A cut-01f switch according to claim 3, said first flanges of the twoarc-quenching members both being adjacent to corresponding sides of saidstrips.

5. A cut-off switch according to claim 3, said first 6 flanges of thetwo arc-quenching members being adjacent to the contact element towardopposite ends of the bridging member and to opposite longitudinal sidesof said strips.

References Cited in the file of this patent UNITED STATES PATENTS

